In message , at 10:33:30 on
Mon, 9 Aug 2010, Chris Tolley remarked:
TfL explained that it could not be aware of any over-charging until
the issue was reported by a passenger.

Apart, of course, from looking for cards where there were two top-up
[bank charges] on the same day.

Yes - some passengers will do that, but that doesn't actually matter.
What you are looking for is top-ups where there were two debits but only
one amount of credit added.

Not holding an Oyster card, I wouldn't know, but in many cases the
financial part of e-transactions is handled separately for security
reasons. If that is the case here, then how would TfL know in detail
about the debits?

That's potentially why you need the people handling the payments to give
you a list (presumably quite a short one) of all the Oyster cards that
requested a debit, and you could then correlate that with the credits
registered against the cards.

Also, this "double dipped" money will also be sitting in some kind of
suspense account, because the books won't balance. In simple terms,
you've got more income than the services you've supplied.
--
Roland Perry